Aft frame with oval-shaped cooling slots and related method

ABSTRACT

An aft frame adapted to interface between a combustor transition piece and a first stage turbine nozzle includes: a closed-periphery frame comprised of a top, bottom and pair of side walls. A plurality of cooling holes or apertures having elliptical or oval cross-sectional shapes are provided in one or more of the top, bottom and pair of side walls, extending axially through the closed-periphery frame. The cooling holes have major and minor axes arranged such that the major axes are substantially parallel with the top and bottom walls.

This invention relates to turbine cooling technology and, morespecifically, to the cooling of an aft frame component interfacingbetween the combustor transition piece and a stage 1 turbine nozzle.

BACKGROUND OF THE INVENTION

A “transition piece” as understood in the context of a can-annularcombustor for a power generating gas turbine, is a duct that connectsthe combustor liner with the first stage nozzle of the turbine. The aftframe is a component which is located at the exit end of the transitionpiece and thus acts as an interface between the transition piece and thestage 1 nozzle. It is exposed to hot gases flowing into the stage 1nozzle and therefore, cooling of the aft frame component is of concern.

More specifically, hot gases flowing through the transition piecerecirculate in a groove between the aft frame and the stage 1 nozzle,causing high thermal gradients. Accordingly, effective cooling needs tobe provided on the trailing face of the aft frame, i.e., that side ofthe frame facing the stage 1 nozzle. Currently, typical aft frameconfigurations incorporate cooling holes with circular cross sections inorder to divert a portion of flow through an impingement sleeve (whichsurrounds the transition piece) into these holes to cool the aft frame.

There remains a need, however, for more effective cooling of the aftframe of the transition piece.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with an exemplary but non-limiting embodiment of thisinvention, oval or elliptical-shaped cooling holes are provided aboutthe periphery of the aft frame. Because oval or elliptical-shaped holesprovide more surface area for effective convection cooling for a givencross-sectional area, cooling of the aft frame is improved.

Accordingly, in one aspect, the invention relates to an aft frameadapted to interface between a combustor transition piece and a firststage turbine nozzle comprising: a closed-periphery frame comprised of atop, bottom and pair of side walls; and a plurality of cooling aperturesextending through one or more of the top, bottom and pair of side walls,the cooling apertures having an elliptical or oval cross-sectionalshape.

In another aspect, the invention relates to an aft frame adapted tointerface between a combustor transition piece and a first stage turbinenozzle comprising: a closed-periphery frame comprised of a top, bottomand pair of side walls; and a plurality of cooling apertures having anelliptical or oval cross-sectional shape provided in each of the top,bottom and pair of side walls, extending axially through the frame; andwherein the cooling apertures have major and minor axes, arranged suchthat the major axes are substantially parallel with the top and bottomwalls.

In still another aspect, the invention relates to a method of forming aturbine aft frame adapted to interface between a combustor transitionpiece and a first stage turbine nozzle comprising: a) providing a closedperiphery aft frame having top and bottom and a pair of side walls; andb) forming elliptical-shaped cooling holes in at least one of said top,bottom and pair of side walls, extending axially through the aft frame.

The invention will now be described in more detail in connection withthe figures identified below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a typical transition piece aft frame ofknown construction;

FIG. 2 is an enlarged detail showing known circular cooling holes orslots formed in the aft frame; and

FIG. 3 is an enlarged detail illustrating the oval or elliptical shapeof the cooling holes to be employed in an aft frame of, for example, thetype shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, an aft frame 10 that serves as an interfacebetween a conventional transition piece (not shown) and a first stageturbine nozzle (also not shown) includes top and bottom walls 12, 14,respectively and a pair of side walls 16, 18 that complete theclosed-periphery frame. Mounting hardware, such as brackets 20 and 22,facilitate connection of the aft frame to the first stage turbinenozzle. The exact manner of attachment is not part of this invention,however, and in any event, any suitable attachment technique may beemployed. It will be appreciated that a conventional transition piece isattached to the opposite side of the aft frame, extending between thefirst stage nozzle and the combustor liner. Examples of this type ofarrangement may be found in U.S. Pat. Nos. 6,412,268 and 6,547,257.

With reference now to FIG. 2, circular cooling holes 24 are typicallyspaced about the periphery of the aft frame, allowing cooling air toflow axially into the holes and through the aft frame, thereby coolingthe frame.

FIG. 3 illustrates a modified cooling hole shape that provides betterand more efficient cooling of the aft frame. Specifically, some or allof the axially extending cooling holes or apertures 26 have anelliptical or oval cross-sectional shape, thus increasing the surfacearea for more effective convection cooling for a given cross-sectionalarea. Elliptical cooling holes or apertures 26 may be used exclusivelyor in combination with circular cooling holes (e.g., holes 24) asdetermined by specific cooling requirements. Dimensions for theelliptical holes may also vary in accordance with cooling requirements.The elliptical cooling holes 26 may be provided in any one or more (orall) of the top, bottom and side walls 12, 14, 16 and 18, respectively,of the aft frame. Preferably, the major axes of the cooling aperturesare substantially parallel to the top and bottom walls of the aft frame.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. An aft frame adapted to interface between a combustor transitionpiece and a first stage turbine nozzle comprising: a closed-peripheryframe comprised of a top, bottom and pair of side walls; and a pluralityof cooling apertures extending through one or more of said top, bottomand pair of side walls, said plurality of cooling apertures having anelliptical or oval cross-sectional shape.
 2. The aft frame of claim 1wherein one or more of said plurality of cooling apertures are providedin each of said top, bottom and pair of side walls.
 3. The aft frame ofclaim 1 wherein said plurality of cooling apertures extend in an axialdirection through said closed-periphery frame.
 4. The aft frame of claim2 wherein said plurality of cooling apertures extend in an axialdirection through said closed-periphery frame.
 5. The aft frame of claim1 wherein said plurality of cooling apertures have major and minor axes,arranged with said major axes substantially parallel with said top andbottom walls.
 6. The aft frame of claim 4 wherein said plurality ofcooling apertures have major and minor axes, arranged with said majoraxes substantially parallel with said top and bottom walls.
 7. An aftframe adapted to interface between a combustor transition piece and afirst stage turbine nozzle comprising: a closed-periphery framecomprised of a top, bottom and pair of side walls; and a plurality ofcooling apertures having elliptical or oval cross-sectional shapesprovided in each of said top, bottom and pair of side walls, extendingaxially through said closed-periphery frame; and wherein said pluralityof cooling apertures have major and minor axes, arranged such that saidmajor axes are substantially parallel with said top and bottom walls. 8.A method of forming a turbine aft frame adapted to interface between acombustor transition piece and a first stage turbine nozzle comprising:a) providing a closed periphery aft frame having top and bottom wallsand a pair of side walls, and b) forming elliptically-shaped coolingholes in at least one of said top, bottom and pair of side walls,extending axially through the aft frame.
 9. The method of claim 8including providing said elliptically-shaped cooling holes in all ofsaid top, bottom and pair of side walls.
 10. The method of claim 8wherein said elliptically-shaped cooling holes have major and minoraxes, and wherein step b) includes arranging said elliptically-shapedcooling holes with said major axes substantially parallel to said topand bottom walls.